My friend decided she wanted to downgrade her iPhone 2G from 3.1.3 to 3.1.2. It worked, but now she gets no service. I have tried restoring her firmware to 3.1.3, but there is still no service. She uses AT&T. Help would be very much appreciated.

I was able to sort of fix the problem. I re-downgraded her back to 3.1.2, still without service. I then jailbroke her phone using blackra1n (still no service) and "upgraded" the phone to the latest version of whited00r. This did not return service. However, I decided to download the unlocked version of whitesn0w in order to try that, and service returned. This makes no sense since she is using AT&T. Although solved for the time being, I would still like help in figuring out what the problem was in the first place and if it is safe to, for example, restore back to the original 3.1.3. I would also like to know what repercussions there are, if any, to using unlocked firmware on the AT&T network.

I'm sure it is also worth pointing out that the problem seemed to stem from the fact that after any restore, whether it was with 3.1.3, 3.1.2, or whited00r (not unlocked), iTunes said it was unable to update carrier settings and gave error 1631. Restoring to the unlocked version of whited00r did away with this error and restored service. Likewise, when I say I did a restore, I mean that I always setup the phone like it was new; I did not restore from backup. When I did restore from backup, it did not fix the problem.

Just use unlocked firmware. I'm guessing you aren't using the SIM provisioned for this particular iPhone? If you aren't, that's strange. At any rate, the latest release of whited00r 4.1 is the best firmware for iPhone 2G's right now. Stick with that.

If I helped you, hit the thanks button please.
You can follow my Twitter @Whited00r
For users with 'older devices ', try custom firmware from whited00r

Just use unlocked firmware. I'm guessing you aren't using the SIM provisioned for this particular iPhone? If you aren't, that's strange. At any rate, the latest release of whited00r 4.1 is the best firmware for iPhone 2G's right now. Stick with that.

The SIM being used is the SIM that came with the iPhone and has worked with the iPhone for a very long time before this fiasco occurred. Thank you anyway.

Have u ever installed idroid on ur phone? im facing this problem too with my i-2g ( sold it already ), In my case i guess maybe it is because of the idroid power management that has not been implement yet so my iphone suffered overheating for a quite long time, so i have replaced the antenna cable - the service is back to normal, for wifi i have put my iphone2g inside a plastic bag and then put it inside my freezer for 10min, and turn it on - the wifi is now ok..